Disc drive units in general are known in the art for use in modern microcomputers such as personal and desktop computers and the like. In the most common form for which this invention is significant, such disc drive units comprise a so-called Winchester disc drive having one or more rotatably driven memory storage discs mounted within a substantially sealed disc drive housing, along with one or more electromagnetic heads for reading and writing data on appropriately prepared surfaces.
A disc drive unit of this type, referred to as a hard or fixed disc drive, is typically available as a compact package with the sealed housing on a rigid chassis frame together with circuit board carrying the necessary drive electronics for interfacing with other components of a computer system. Within the drive, one or more discs are rotated at a constant speed by a spindle motor. Data is stored on a plurality of tracks defined on the surface of the discs. As the discs rotate, actuator arms fixedly mounted on a pivot cartridge move the electromagnetic heads from track to track under control of a voice coil motor having a moving element supported from the same pivot cartridge. This pivot cartridge is supplied as a single integral assembly which is typically mounted into the base of the disc drive. The actuator arm or more typically arms are supported from the cartridge and extend from the cartridge toward the discs; a v-shaped assembly, extending in the opposite direction to the actuator arms, supports the coil for the voice coil motor. Assembly of the actuator arm assembly begins with the pivot assembly which includes the bearings about which the actuator arm will rotate and inner and outer sleeves therefore. A flange is at the top of the pivot bearing assembly; then the actuator arms are stacked on, together with an appropriately located coil support arm; a locking nut is threaded onto the bottom to hold all the above elements together by friction.
However, with reduction in size of disc drives, the pieces of the actuator arm and voice coil support have become smaller, thinner and lighter in weight. As such, it has become increasingly difficult to apply sufficient frictional force against the adjacent pieces merely by screwing the locking nut tightly down against the stack without damaging or torquing out of shape the adjacent pieces. Moreover, even as disc drives have become smaller and formed of lighter weight components, the need for more rapid accessing of the data stored in the discs by quickly moving the actuator arm to position the transducer it supports from track to track has become greater.
The motion of the actuator arm is accomplished by energizing the voice coil motor, and more specifically by passing a current through the coil supported by the v-shaped assembly from the same pivot cartridge which supports the actuator arms. This actuation both begins and ends very quickly, resulting in the imposition of significant forces to both the coil and the arm as it is accelerated and decelerated. Yet in spite of the magnitude of the forces, it has become even more critical that there is absolutely no motion of the coil and/or arms relative to one another.